Strain relief device



0d. 12, 1943. EBY 2,331,313

STRAIN RELIEF DEVICES Filed Sept. 15, 1938 INVENTOR HUGH HEB).

I lad/4 45mm ATTORNEY Patented Get. 12 1943 STRAIN RELIEF DEVICE Hugh H. Eby, Jenkintown, Pa., assignor to Penn Electric Development Corporation, Philadelphia, Pa., a corporation of Pennsylvania Application September 15, 1938, Serial No. 230,091 1 3 Claims.

This invention relates to strain relief devices, and particularly to devices for application to electric conductors to absorb tensioning strains impressed upon the conductors, relative to housings, mountings or terminals for the conductors.

In the low voltage electrical field, it is common to provide cords and disconnecting plugs attached thereto and arranged for more or less frequent connection and disconnection from the sockets of electrical appliances. In the past, the tensile strain required for the disconnection frequently has been placed upon the current carrying wire in the cord, usually having a focal point for the stress at the connection. of such wire with the screw .or other anchor to the metal element of the terminal. Repeated attachment and detachment by withdrawing tension on the cord ultimately stresses the wire to the point of rupture at or adjacent to the screw, resulting in open circuits, shortcircuits, and in fire hazards, especially in the case of domestic appliances. Obviously similar disadvantages maintain in the case of permanent wire connections to the base of a lamp, fan, or the like, in that through accidents, falling and tripping over, or dropping articles upon the wire connections similar separating strains areimparted to the points of attachment of the wire or ,cord.

It is among the objects of the invention: to provide an improved strain relief device; to provide a strain relief device which retains a firm grip frictionally without additional fastening or securing means; to improve the art of strain reliefs; to provide a mounting device for operative association with a strain relief and a mounting support in a novel and eificient manner; to provide a strain relief which relies upon distortion of the cord for part of its frictional effect; to provide a strain relief which is effective against both torsion and tension; to provide a strain relief of extreme economy of manufacture and applications; to provide a strain relief comprising an open jawed member having a plurality of inclined teeth such as to resist retraction from the wire in a direction opposite to the direction of attachment; to provide a strain relief comprising an open jawed inwardly toothed element arranged to frictionally grasp a wire and to resist movement on the wire in any direction; to provide a strain relief comprising a pair of oppositely disposed open jawed inwardly and rearwardly toothed devices arranged to frictionally engage a wire and to frictionally remain in engagement therewith without additional securing devices, to resista maximum pull; and

many other objects and advantages as will become more apparent as the description proceeds.

In the accompanying drawing forming part of this description:

Fig. 1 represents a plan of a preferred form of strain relief element of value of and by itself, and of particular value when used with a duplicate or complemental element, turned at thereto.

V Fig. 2 represents a plan of a modified form of relief element, also usable singly or in duplicate.

Fig. 3 represents a side elevation partially in section, of an appliance base, witha metallic attaching pan anchored to both the base and a fragmentary portion of a connector or wire cord, to anchor the cord byits housed strain relief to the wall of the base. I

vFig. 4 represents a transverse section through a wire connector with the form of strain relief element shown in Fig. 2 in duplicate in the pan device of Fig. 3. l I

Fig, 5 represents a fragmentary side elevation of the same.

Fig. 6 represents a fragmentary perspective of the same.

Fig. 7 represents a; transverse diametric section through the same. a

Fig, 8 represents an enlarged fragmentary side elevation of a portion of connector or cord with a pair of the relief elements of Fig. l, or the like disposed in anchored contiguous relation thereof, as accomplished manually, or by any suitable machine.

Fig. 9 represents a transverse section through the cord shown in Fig. 8, with the'pair of relief devices of Fig. 1 in anchored engagement thereon.

It is to be understood that the strain relief elements may be made of various materials, including various kinds of metals, for certain installations, but that in the main it is preferred that some insulating and relatively cheap material such as vulcanized fiber, or a phenolic condensation product, will be used. Usually and preferably it is such as conduces to production by stamping operations.

Referring, to Fig. 1, the element In is preferably and generally U-shape in plan, having the central connecting web portion H, the inner surface I2 of which is preferably generally arcuate or curved to receive, although not necessarily to fit, the curved surface of the wire toibe engaged. From the median or central portion H, a leg l3 extends, having the internal rearwardly extending pointed serrations or teeth I4, and having the outwardly flared guiding mouth portion l5 terminating in a rearward shoulder or supplemental tooth 9. Tooth 9 may be undercut, or be substantially square as shown. On the outer surface, the element may be substantially round or any other shape such as oval, or angular and it may have the ear IE or the like to assist in prevention of rotation of the element in a suitable support as will be later described. Generally parallel to leg |3, in spaced relation thereto, the leg I1 is disposed having the rearwardly or inwardly projecting teeth I8 or serrations, having the outwardly flared mouth surface complemental to opposite surface l5, so as to guide a wire between them. Its outer surface, substantially diametrically opposite to'ear I6, has the ear 2|, Guide surface 20 terminates in the undercut or square tooth l9. It will be observed that the two spaced legs respectively l3 and I1 have such relation as to effect a wire cord receiving slot 22 having the flared guiding mouth defined by the outward surfaces l5 and 20 re- 'spectively. It is to be observed that the slot preferably has appreciable length, at least greater than the radius of the disc and has inward rearward teeth on both sides.

In Fig. 2, the substantially annular element 23 may have the arcuate outer surface shown, or may have the ears l6 and 2| of Fig. l, or the like disposed diametrically on the element or, as may betrue of all forms, it may have a polygonal outline if desired.

inwardly the element 23 has a slot 24 formed by the legs 25 and 26, and the surface of which is formed of the outer flared surfaces 21 and 2 respectively, and the inwardly directed rearwa-rdly extending serrations or teeth and 3|,

respectively. On the connecting web portion 29, in line with the slot 24, is the spike or pointed tongue 32, arranged to divide or separate portions of an impaled cord, to force the portions laterally into locked engagement with teeth 38 and 3| as will be clear, or will become so as the description proceeds.

Externally element 23 is shown as having a plurality of diametrically oppositely disposed angular notches, as at *61. The notches 61 are for the purpose of facilitating anchoring engagement of strain element 23 with its ultimate support on another element or the prevention of relative rotation of the relief element and its ultimate support.

It will be apparent that with the assembly of Fig. 4, it will be possible to dispose another duplicate element such as is shown in that figure or in Fig. 1 with suitable external contouring in parallel contiguous but reversed relation on the connection, so that the slot 24 of the first element is mounted on the wire adjacent or contiguous to the above element, and so that when both are forced upon the wire, the lateral notches 61 of one element will register with the respective notches '61 of the'second mentioned reversed element.

It will be apparent that either of the elements shown in the figures may be used as above to good effect. Thus element ll! of Fig. 1 and element 23 of Fig. 2 may each be forced laterally upon a connector until an edge thereof, engages the inner surface of the element, at l2 in Fig. l, or impaled on the spike 32, of Fig, 2, respectively, to lateral impalement upon the rearwardly pro- Jecting teeth 9, l4, l9 and I8, of Fig. l, or 38 and 3| of Fig. 2 with such biting engagement in the insulators of the connector that it requires a veritable tearing of the insulation to secure fingers 82.

relative axial movement of the wire or connector and the strain relief element. It will be understood that the anchoring engagement between the strain relief and connector is considerably enhanced by providing the elements in complemental relatively reversed pairs, as shown in Figs. 4, 8 and 9, the strain relief elements ID of Fig. l are provided in reversed duplicate and each reinforces the other and enhances its relative anchoring effect. It is to be noted that the rearward teeth have insulation and the like squeezed upon them to insure anchoring. It is an interesting fact that instead of the close adjacency shown in Fig. 8, it is sometimes a means to an even better anchorage if the planar members are slightly separated so that insulation may be distorted from the surface between the elements, as it piles up on the teeth of the complemental element. It has been found possible at least to double the tensile strength of a single element by arranging them in pairs, either in contacting adjacency or in slightly spaced relation.

It is preferred in the interest of both economy and gripping power, that the discs or planar strain relief elements be relatively thin- This makes the rearward teeth sharp to facilitate entry with the insulators of the connectors. Of course the material should be thick enough to furnish sufficient strength for the tensile requirements.

As shown in Fig. 3 the base of a fixture such as a fan, telephone, lamp, etc. has a wall 56, having an aperture 51, such as to receive axially, the sheet metal pan 58. The pan is arranged for a tight sliding fit in the aperture and is preferably open-bottomed having an axial aperture '59 of appreciable diameter, including a flange of narrow extent formed on one end, and having the plurality of flange fingers in two radially staggered series, relatively long fingers E1, in staggered relation to the relatively short Preferably the long fingers 8| arise out of radially indented or recessed portions 64 forming internal ribs 63 arranged to rest in registering locking recesses 81 on the complemental strain relief elements 23.

When applying the assembly of a pair of strain relief elements 23 to a wire conductor 20, the cage or pan 58 is threaded over the wire, then the two strain relief elements are forced laterally on the wire until their respective lateral recesses '6! are caused to register (at which time the elements have been forced to frictionally grip the wireo'r connector) then the :pan 58 is slid axially on the wire and over assembled relief elemerits the i'ecossed portions or internal axial ribs 63 engaged in registering recesses and the pan engaging and covering the lateral edges or both elements after which the short legs 62 are turned over against the adjacent element 23, to hold the two elements .23 between fingers 62 and flange 6|], with the wire 20 running through apertur'e 59 of the pmn. The housed Strain relief is then mounted frictionally in the opening 51 of the mounting support and fingers 5| are "bent outwardly to anchor the .pan and relief in the base 55.

It is to'be understood that either of the toothed forms of strain reliefs may be used in the pan assembly just described and such use is contemplated.

It is to be understood 'thaitthe ears |6 and 2| of the element of Fig. 1, are such 'as to be capable of being grasped or gripped by securing 'or anchoring devioes attached to the ears alone,

if desired, or as eccentric elements on the connector such as to abut suitable stops to prevent rotation of the connector and strain relief ele- .ments in an assembled terminal device.

I claim as my invention:

1. A strain relief comprising a fiat disc-like element having an insulated conductor receiving slot extending from an entrance in the outer edge thereof and terminating in a closed end, the slot having an inner enlargement wider than the slot entrance, the opposing walls of which slot comprise in part at least acutely angled inclined teeth pointing toward the closed end with the pointed ends of the teeth in substantial alignment with the respective walls of the entrance of the slot, whereby the insulation of an insulated conductor pushed laterally into the slot against the closed end thereof in contact with the teeth is substantially pierced by the teeth and is disposed between the teeth, and between the teeth and the closed end of the slot to hold the conductor against torsional, lateral withdrawal and axial slipping movements.

2. A strain relief comprising an element having a pair of spaced legs and means connecting the legs together at one end forming an insulated conductor receiving slot, said slot having an internal enlargement, inwardly directed acutely angled teeth formed on the legs and extending into the slot with the teeth pointing toward the closed end of the slot with the points of the teeth closer together than the enlargement surfaces and. in substantial alignment with the respective surfaces of the slot at its entrance, a supplemental impaling tooth mounted on the connecting means and substantially bisecting the slot, the impaling tooth and adjacent teeth on the respective legs being so disposed that when an insulated conductor is forced into the slot to impalement on the impaling tooth, the insulation of a conductor is laterally distorted in the enlargement to en- 7 gage and be anchored by the said adjacent teeth and held against torsional, lateral withdrawal or axial slipping movements relative to the element.

3. In strain reliefs an anchoring housing for mounting a strain relief operatively to the aperture in a supporting plate comprising a flat apertured Wall against which a strain relief can abut laterally, the wall merging into a drawn continuous peripherally closed short cylindrical wall for engaging the peripheral edge of the strain relief to be associated therewith, said cylindrical wall having integral bendable fingers arising out of a free edge thereof arranged in an annular series and arranged to be bent radially inwardly to enclose such strain relief by engaging another lateral surface thereof from that engaged by the flat wall, said cylindrical wall having a plurality of axially extending indentations forming external recesses and internal ribs, the free edge of thecylindrical wall being continued in a plurality of fingers aligned with the respective indentations and forming an annular series of smaller diameter than that formed by the first mentioned fingers and arranged for radial outward bending across and beyond the first mentioned annular series of fingers.

HUGH H. EBY. 

